its cause when the alpha 1 antitrypsin protein has mutated, changing the shape of the active site, so chloride ions can't enter mucus through the "alpha 1 antitrypsin" channel protein,. if the ions could enter the mucus it would lower the water potential of the mucus so then water would pass into it over a concentration gradient making the mucus runny, like normal

Cystic fibrosis is an inherited disease of the mucus glands. It causes chronic, progressive damage to the respiratory system, chronic digestive system problems, and can affect other organs.

The signs and symptoms of this disorder are caused by the production of abnormally thick, sticky mucus in the body's organs. Problems with breathing are among the most serious symptoms. Mucus can obstruct the airways and cause bacterial infections in the lungs, leading to chronic coughing, wheezing, and inflammation. Over time, mucus buildup and infections lead to permanent lung damage, including the formation of scar tissue (fibrosis) and cysts in the lungs.

Most people with cystic fibrosis also have digestive problems. Mucus can block the ducts of the pancreas, preventing enzymes produced by that organ from reaching the intestines to help digest food. Problems with digestion can lead to diarrhea, malnutrition, and weight loss. Some babies with cystic fibrosis have meconium ileus, a blockage of the intestine that occurs shortly after birth.

Infertility, or the inability to conceive a child, is common in men with cystic fibrosis, but infrequent in women with the condition.

Mutations in the CFTR gene cause cystic fibrosis.

The protein made by the CFTR gene (The official name of this gene is “cystic fibrosis transmembrane conductance regulator, ATP-binding cassette (sub-family C, member 7).”) forms a channel that controls the movement of salt and water into and out of cells. Mutations in the CFTR gene alter this protein in such a way that the channel is blocked. As a result, cells that line the passageways of the lungs, pancreas, and other organs produce the abnormally thick mucus characteristic of cystic fibrosis.

Other factors likely influence the course of the condition. For example, changes in genes other than CFTR might help explain why some people with cystic fibrosis are more severely affected than others. Most of these genetic changes have not yet been identified, however.

The CFTR gene provides instructions for making a protein called the cystic fibrosis transmembrane conductance regulator. This protein functions as a channel across the cell membrane. Such channels are found in tissues that produce mucus, sweat, saliva, tears, and digestive enzymes. Chloride, a component of salt, is transported through the channels in response to cellular signals. The transport of chloride helps control the movement of water in tissues and maintain the fluid consistency of these secretions. Proper functioning of these channels ensures that organs such as the lungs and kidneys function properly.

This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder are carriers of one copy of the altered gene but do not show signs and symptoms of the disorder.